1. Field of the invention
The present invention relates to a process for the production of dihydric phenols, such as resorcin etc., in particular, by oxidizing diisopropylbenzenes followed by acid cleavage of the resulting dihydroperoxides.
2. Desrciption of the Prior Art
It has been known that hydroperoxides, such as, diisopropylbenzene dihydroperoxide (DHP), diisopropylbezene monocarbinol monohydroperoxide (HHP), diisopropylbezene monohydroperoxide (MHP) and so on, are produced together with carbinols, such as, diisopropylbezene dicarbinol (DC) and so on, by oxidizing diisopropylbezenes with molecular oxygen in the presence of a base.
It has also been well known that industrially useful chemicals, such as, resorcin, hydroquinone and so on, can be obtained by subjecting DHP to an acid cleavage using an acid catalyst, such as, sulfuric acid or so on, in the presence of an aromatic hydrocarbon solvent, such as toluene etc., or a ketone solvent, such as, acetone, methyl isobutyl keytone (MIBK) or so on.
While these prior techniques can be employed as a useful process for obtaining resorcin and hydroquinone from diisopropylbezene, there has been a strong demand for producing hydroperoxides, especially DHPs at higher yeild by oxidizing diisopropylbezene more efficiently in order to obtain resorcin or hydroquinone at a more higher over-all yield from diisopropylbezene.
Attempts had been proposed for converting the carbinols, such as, HHP, DC etc., present in the reaction product mixture of the oxidation of diisopropylbezene further into DHP by oxidizing them by contacting the product mixture with hydrogen peroxide (H.sub.2 O.sub.2), as disclosed, for example, in the British Patent No. 910,735, in the Japanese Patent Application Lay Open Nos. 23939/1978, 53265/1980 and so on. According to the disclosures of the above Japanese Patent Application Lay Open Nos. 23939/1978 and 53265/1980, it is taught that dihydric phenols can be obtained in a high efficiency by oxidizing carbinols, such as, HHP, DC and so on, with subsequent acid cleavage of the oxidation products, by conducting the process step of oxidization of the carbinols into DHPs with hydrogen peroxide separately from the process step of acid cleavage of the DHPs into the corresponding dihydric phenols.
In summary, the prior technique for the production of dihydric phenols, such as resorcin etc., by oxidzing isopropylbezenes with subsequent acid cleavage of the oxidation product proposed previously has been based on the following reaction scheme:
Upon oxidizing diisopropylbenzenes with molecular oxygen in the presence of a base using, if necessary, a radical initiator, a reaction mixture containing DHP, HHP, MHP, DC and so on as explained above is obtained. This oxidation product mixture is then subjected to a further oxidation with hydrogen peroxide in order to oxidize HHP, DC and so on contained in the product mixture into DHP in a heterogeneous reaction system consisting of an oily phase of an aromatic hydrocarbon solvent, such as toluene etc., containing dissolved therein said oxidation product mixture and of an aqueous phase containing hydrogen peroxide and an acid catalyst, such as sulfuric acid, by contacting the two phases with each other. Then, the so formed DHP is subjected to an acid cleavage in a separate process step to convert it into the corresponding dihydric phenol, such as resorcin or so on.
The process step of oxidizing the HHP, DC and so on with hydrogen peroxide into DHPs may be realized by supplying the product mixture of oxidization of diisopropylbenzene in a form of an oil phase containing said product mixture in an aromatic hydrocarbon solvent, such as toluene etc., to a tank reactor equipped at its top with a distillation column and a water separator, while supplying to this reactor simultaneously hydrogen peroxide and an acid catalyst, such as sulfuric acid, in a form of aqueous phase, so as to cause the two phases to contact with each other in order to effect oxidation of the said HHP, DC etc., by hydrogen peroxide at a temperture of 20.degree.-70.degree. C. Then, the oily phase in the resulting reaction mixture is separated from the aqueous phase and the aqueous phase is recirculated to the reactor under supplement of the consumed hydrogen peroxide and the acid catalyst, while the oily phase is supplied to the subsequent acid cleavage step after it has been neutralized and concentrated. It was proposed to supply hydrogen peroxide to the reactor in an amount of about 16 moles per mole of HHP. Here, the weight ratio of oily phase to aqueous phase in the reactor is maintained at a value of about 1.6. The reaction water formed by the oxidation of HHP is removed fromm the reaction mixture by an azeotropic distillation with the aromatic hydrocarbon under a reduced pressure to the outside of the system, wherein the aromatic hydrocarbon is recirculated to the reactor. In the above procedure, it is necessary to maintain the reaction temperature by supplying vapor of an inert solvent for avoiding any detrimental influence due to localized heating. The reason why the ratio of oily phase/aqueous phase is to be maintained at about 1.6 in the reactor is such that the acid cleavage of the peroxide will scarcely occur when an ample aqueous phase is present, even if a concentrated acid catalyst resulting from the concentration of the aqueous phase may come to contact with the reaction liquor. However, use of large amount of water is not preferable, since predominant part of the by-products is transferred to the aqueous phase which accumulate therein after repeated recirculation cycles. In addition, it is necessary to maintain the concentration of hydrogen peroxide in the reaction system at about 16 times of HHP in mole ratio due to employment of large amount of water.
Thus, the prior technique of oxidizing HHP, DC and so on by hydrogen peroxide into DHPs has disadvantages, since quite large amount of hydrogen peroxide relative to the amount of HHP etc., should be supplied and laborious and uneconomical procedures of dehydration by an azeotropic distillation under a reduced pressure and recirculation of the aromatic hydrocarbon are necessary, beside the necessity of controlling the concentrations of hydrogen peroxide and of the acid catalyst for the requisite recirculation of the aqueous phase with simultaneous demand of large amount of water for maintaining the ratio of oily phase/aqueous phase at a lower value in oder to conduct the operation smoothly.